Field
This invention relates to marine gas scrubbers and ballast water disinfection systems. In particular, it relates to a combination marine exhaust gas scrubber and ballast disinfection system using seawater/water surrounding a ship to reduce/scrub smoke-stack emissions and produce a disinfected seawater/water for ballast, which can then be periodically or continually discharged back into the seawater/water body without concern for the spread of non-invasive species.
Statement of the Art
Numerous marine gas scrubbing systems are known to meet the new IMO regulations for controlling shipping vessel air pollution, which require significant reduction in sulfur oxides (SOx), nitrogen oxides (NOx), and carbon dioxide (CO2) emissions. There are several types of wet and dry scrubber exhaust gas cleaning systems (EGCS) for reducing air emissions having different advantages and disadvantages1. 1 See Wet or Dry? Which Scrubber Type will Reign Supreme? by Maryruth Belsey Priebe, International Quality and Production Center, www.jadecreative.com/media/13881/Wet or Dry—Which . . .
“Wet scrubbers use either fresh or sea water to remove gas impurities. The wastewater is then discharged into the sea or retained within a closed loop when discharging it is not permitted. An open loop sea water system is a passive solution in that it has very few moving parts and requires hydraulic pressure provided by a pump in order to run. The system includes pumps and strainers, was water filters, sludge handlers, effluent monitors, and exhaust gas monitors.
In an open loop system, waste water is simply put overboard while at sea. This type of system requires regular maintenance, de-fouling, and operational checks, but is otherwise low maintenance. It also doesn't need a great deal of space for storage of waste material.
In a closed loop fresh water wet scrubbing system, there's a buffer tank, a heat exchanger, pumps and strainers, a sodium hydroxide unit, and water treatment device. Like the open system, there are no internal moving parts, and other than occasional inspections there is very little maintenance required. One disadvantage of this option, however, is that it requires storage space (the buffer tank) to hold waste water until it can be discharged.
The downside to using a wet scrubber is that it cools the exhaust gas, a problem that's not faced by dry scrubbers. Additionally, with wet scrubbers, selective catalytic reduction systems must operate before the scrubbers. Fitting all of this together, especially for dual-fuel engines can be quite complex.
Dry scrubbers also effectively remove exhaust gas pollutants, but they employ a filter or bed of granulated hydrated lime. The chemical reaction between the SOx and the lime creates calcium sulfate which can then be disposed of as solid waste when the ship reaches a port.
A dry scrubber offers several advantages. First, this type of system does not result in the production of liquid effluent that must be disposed of overboard. Of course, most importantly, dry scrubbers will reduce NOx emissions substantially, however, on the downside, dry scrubbers require significant onboard storage to handle the dry bulk reactants and products associated with the process.”
Patterson, US 2018/0154309 published Jun. 7, 2018 is an example of a low pressure drop Exhaust Gas Wet Scrubber produced by Belco Technologies Corporation, a DuPont business unit shown in FIG. 1, attached. The Belco scrubber system includes an in-line, wet scrubber located in the funnel of the ship. The scrubber includes a generally cylindrical housing having an inlet fitting at the bottom longitudinal end of the scrubber housing and an outlet fitting at a top longitudinal end of the scrubber housing. The overall shape of the scrubber in its normal (vertical) operating position fits within the funnel.
The scrubber can function to silence engine noise, thereby replacing the function of a silencer. An exhaust mixer is mounted directly on the scrubber inlet so that the exhaust of multiple engines may be serviced by one scrubber.
The Internal components of the scrubber have an inlet fitting that extends into the interior of the housing and opens in the interior at a mouth. The mouth is covered by a diverter cap that prevents water used in the scrubber from entering the mouth. A tiered lower absorber spray head, a middle absorber spray head, and an upper absorber spray head each include nozzles to spray water within the scrubber housing. A droplet separator is located near the top of the housing to capture entrained water droplets. The droplet separator includes rows of curved pieces (sometimes called “chevrons” for their general shape) that define tortuous paths for scrubbed exhaust gas leaving the scrubber facilitating water droplet removal. A wash sprayer located under the droplet separator is periodically activated to spray water or other solution through nozzles for cleaning the chevrons forming the droplet separator.
A heat exchanger or hot air injector may also be provided near the outlet fitting to heat the exiting exhaust gas for reducing a water vapor plume leaving the scrubber system. In one embodiment, the internal components are constructed so that the scrubber can run dry with internal components sufficiently robust as to withstand hot exhaust gas not cooled by any water flowing within the scrubber.
In use hot, dirty exhaust gas from one or more of the engines enters the inlet fitting of the scrubber and exits the mouth within the scrubber housing. In some instances, the entering exhaust gas might be on the order of 350 degrees C. The diverter cap alters the flow of exhaust gas from a generally vertical direction to a generally lateral direction. The diverter cap also redirects water coming down from the lower, middle and upper absorber spray heads laterally off of the sides of the diverter cap. The hot exhaust moving out from under the diverter cap passes through a curtain of water around the diverter cap. A substantial amount of water is evaporated so that much of the heat of the exhaust gas entering the scrubber is removed immediately upon entry into the interior of the scrubber housing. The quenched gas and entrained water flows upward from the diverter cap in the housing. In addition to providing further cooling of the exhaust gas, the water captures particulates in the gas. A reagent may be added to the water sprayed from the lower, middle and upper absorber spray heads to promote the absorption of a particular pollutant by the water. For example, a reagent may be added to promote absorption of SO2. Water droplets entrained in the gas flow passing above the upper absorber spray head encounter the droplet separator. The changes in direction of the gas flows passing through the tortuous paths defined by the chevrons of the droplet separator promotes collection of water droplets from the gas flow on the surfaces of the chevrons. Collected water on the chevrons may fall down toward the bottom of the scrubber housing. Water containing particulates and SO2 from the droplet separator and from the lower, middle and upper absorber spray heads falls down within the scrubber housing to a slanted floor at the bottom of the housing. The floor is located well below the mouth of the inlet fitting to inhibit water collected at the bottom of the housing from entering the inlet fitting. A drain outlet is located on the lowest side of the slanted floor to permit dirty liquid to exit the scrubber for disposal.
These wet scrubbers are not designed to disinfect ship ballast water using sulfur dioxide. Gong et al., U.S. Pat. No. 8,449,778 issued May 28, 2013 discloses a method of treatment ballast water with sulfurous acid to kill invasive species and remove oxygen from the ballast water to preserve hulls from rusting, while preventing contamination of discharge waters with invasive species.
There thus remains a need for a hybrid combination marine exhaust gas scrubbing and ballast water disinfection system. The system described below provides such a system.